Video on Demand (VoD) or Audio and Video on Demand (AVoD) system allows clients to select and play video or audio content on demand. IPTV technology is often used to bring video on demand to televisions and personal computers.
Sometimes, the limited transmission resource, such as bandwidth etc. at the side of VoD server does not allow for a large scale of clients simultaneously.
In order to more efficiently make use of the limited resource, a solution is described in the published PCT application WO2008083523, which provides a scheduling method for a VoD server of 2D video content (or 2D content to shorten the description). A 2D content is divided into pluralities of portions or blocks. The method reschedules the transmission of portions of a requested 2D content for a requesting client and uses multicast to transmit, so that some portions can be shared among those clients requesting the same 2D content. Specifically, the method comprises the steps of receiving a request for a 2D content and generating a schedule for delivering the 2D content with a first delay for an initial portion of the 2D content and with a second delay for a subsequent portion of the 2D content. The step of generating the schedule comprises selecting a first delay to minimize the time period from receiving the request to delivering of the initial portion of the 2D content, and selecting the second delay to satisfy a delay parameter associated with the request while also increasing a delay for starting delivering the subsequent portions. Herein, the second delay makes subsequent portions be transmitted as late as possible but it shall be selected in such a way that the content received by the client's side can be played continuously or at least without unacceptable interruptions.
In 3D systems, a left eye view and a right eye view (or called left view and right view) at the client side are used together to generate a stereoscopic view. In order to transmit the left view and the right view to the client side, the most straightforward way is to transmit the left and right eye views as completely independent data streams. An alternative is to transmit 2D video plus metadata, and the metadata represents the information in the third dimension.
There are 2 types of 2D plus metadata: 2D plus Delta (or 2D plus Difference) and 2D plus Depth (or 2D+Z). With regard to 2D plus Delta, it is a standard-listed methodology as part of MPEG2, and MPEG4, specifically on the H.264 implementation of Multi-view Video Coding extension. It utilizes the left view or right view (sometimes they are also called left channel and right channel) as the 2D version (or called 2D part) and the optimized difference or disparity (Delta) between left and right views is injected into the video stream as client data, secondary stream, independent stream, or enhancement layer. So with the 2D version and the Delta, a stereoscopic view can be generated. The Delta data can be either a spatial stereo disparity, temporal predictive, bidirectional or optimized motion compensation. With regard to 2D plus Depth, each 2D image frame is supplemented with a depth map which indicates if a specific pixel in the 2D image needs to be shown in front of or behind the screen plane. The 2D plus Depth is supported by the MPEG standards. MPEG-C part 3 allows depth map to be treated as “auxiliary video” and compressed with existing video coding techniques (e.g. H.264/AVC).
In 3D systems, the most used format is 2D plus metadata which can be easily integrated into existing content distribution and management systems, such as VoD via cable, satellite, Internet or terrestrial broadcasting. And it is backwards compatible with legacy 2D set-top boxes and is independent of display format. In these 3D systems, 2D and metadata are usually multiplexed and transmitted through a single channel or data stream. Therefore, 3D VoD service can be easily provided by using some existing 2D content delivery systems. Many companies provide 3D VoD service in this way, such as Numericable, Virgin Media, Philip, etc.
Transmitting 2D plus metadata in two different channels or data streams allows coexistence of 2D video player and 3D video player. A viewer who has a 2D video player will only receive 2D data and view the 2D video normally. He can choose whether to receive the associated metadata or not, which is impossible if 2D and metadata are multiplexed. A viewer who has a 3D video player will receive both 2D data and metadata.
But the conventional methods for transmitting 2D plus metadata do not efficiently make use of the bandwidth, thus, it is desired a method to efficiently transmit the 3D content among clients requesting the same 3D content.